Would it be possible for the TIPI to do more than just midi? Like maybe have it send commands to a Sound Blaster or Adlib emulator running on the Pi? And then route the output back through the expansion port's audio pass through?

Does the TI do any processing on the input from audio line on the side port, or does it just pass it directly to the audio pin on the av cable?

In other words, if you took an audio cable, stuck one end into the trrs jack on the PI 3B+, then modified the other end to connect it to the audio input pin on the TIPI, could you then start up a music player on the PI and have it play through the TI's audio out?

Does the TI do any processing on the input from audio line on the side port, or does it just pass it directly to the audio pin on the av cable?

In other words, if you took an audio cable, stuck one end into the trrs jack on the PI 3B+, then modified the other end to connect it to the audio input pin on the TIPI, could you then start up a music player on the PI and have it play through the TI's audio out?

But to answer this, the answer is 'essentially yes'. The audio runs through the sound chip and is mixed there, but there are no gates between the side port and the audio output, so as long as the level is correct it should be heard.

Thanks for the links, but attempting to load any TI related pages from unige.ch all I get is a 404: page not found.

Tried looking through that pdf, but I know nothing about deciphering schematics so it's all a bit beyond me.

The links work for me. If you are cutting and pasting or typing them, you must include everything through “ti99” or a search is unlikely to find the tech pages.

Edit: The second link is malformed. Here it is again: http://www.unige.ch/medecine/nouspikel/ti99/cassette.htm. Also, you must click on the link because AtariAge often reduces the displayed size by replacing part of the full link with an ellipsis. For example, the last link in full, with ‘/’ replaced with ‘|’ to prevent AA’s shortening, is http:||www.unige.ch|medecine|nouspikel|ti99|cassette.htm.

After asking about the trrs jack on the pi board I've done a little experiment. I picked up a mono audio cable and a socket. Soldered some leads to socket and connected it to the audio in and one of the ground pins on the TIPI. Telnetted into the PI and installed omxplayer, which I then used to play a few mp3's through the TI's audio out.

Seemed to be working fine at first, but halfway through one of the mp3's the TIPI telnet app froze the TI and the music cut off. After rebooting the TI everything seems fine so I'm not sure what that was about